Conventional powder guns can fire subcaliber projectiles inserted in protective and obturating casings, or sabots, which can be discarded on exit. Sabots allow firing projectiles with different cross sections from the same gun, considered a valuable capability. The diameters of the projectiles cannot exceed the fixed gun barrel caliber, a self-evident limitation of this technique. Electromagnetic launchers also accelerate launch packages in which subcaliber projectiles are inserted in sabots, with the same limitation.
Electromagnetic launchers are being developed to accelerate various projectiles to high velocities not achievable by conventional guns. Other potential applications include accelerating self-propelled missiles, decoys, torpedoes and other massive objects, to lower velocities but on relatively short launch paths. When matured, electromagnetic launchers may find uses in commercial applications (e.g., rock pulverizing in mines was considered in the U.S. Pat. No. 7,634,989).
Pulse power sources energizing electromagnetic launchers, such as capacitor banks or rotational electrical generators, can release very large amounts of energy, currently approaching 100 MJ, in short pulses of high current on the order of millions of Amperes, typically in 3-10 millisecond duration range for high velocity launchers. Together with their pulse forming networks, pulse power sources are the heaviest, bulkiest and most expensive part of electromagnetic launch systems. It would be advantageous for such systems to fire launch packages of various transverse sizes using a single pulse power source with sabots sized appropriately for different projectiles, small and large, reducing waste associated with accelerating oversized sabot used to fit a smaller projectile with a large caliber barrel.
While it is possible to use with a single pulse power source several electromagnetic launchers with different fixed calibers, a versatile launcher capable of adopting a variety of launch packages would in many cases be preferable. One attempt to address this need, the U.S. Pat. No. 4,901,620 issued to G. A. Kemeny provided a railgun having several bores of different calibers in a single barrel as shown in FIG. 1. Kemeny's solution, however, has its own shortcomings related to the oversized barrel.